This invention relates to cathode ray tube (CRT) video display devices such as for use in broadcast television receivers.
Various proposals exist for the transmission, reception and display of signals representative of pictures with higher aspect ratios (the ratio of width to height) than the conventional 4:3. For example, the MAC family of systems (multiplexed analogue components) includes provision for transmitting signals with aspect ratios of e.g. 5.3:3 or 16:9 by compressing the horizontal luminance and chrominance information by more than the 3:2 and 3:1 compressions, respectively, normally applied. Such altered compression ratios would be signalled to the receivers by inclusion of a special `flag` in the signal broadcast by the transmitter. Suitably-equipped receivers with a 4:3 aspect-ratio display could then display the centre part of the picture, with marginal information at the sides of the picture being lost. This is illustrated in FIG. 3 of the drawings, where `lost` information is indicated by shaded areas.
It has also been proposed to transmit in the signal a code indicating the region of the picture where the main action is at any instant. This allows such a receiver to follow the action in a programme, or pan, and select any particular 4:3 picture from the wider-screen picture to fill the display, under the control of the code entered by the broadcaster. This is illustrated in FIG. 4, showing an instant when the lost information is all at one side of the picture.
Another, but generally less acceptable, possibility is to fill the 4:3 display with the entire wide-screen picture, resulting in an anamorphic distortion to the picture geometry, as shown in FIG. 5.